To ensure high comfort from the viewpoint of the sensation of heat in areas of contact with the seat, the utilization of active heat-regulation systems is known, i.e. systems comprising a fan that is located beneath the squab and which feeds a flow of air from the passenger compartment towards the inside of the squab or in the opposite direction to increase heat exchange and thus the removal of heat.
Known solutions of the active type are not very satisfactory, as the sensation perceived by the user is not always positive.
In fact, when first using the seat, the user tends to perceive an immediate sensation of discomfort that becomes even more evident the higher is the initial heat exchange between body and seat. Due to the large and sudden removal of heat by the fan, the user perceives a sensation of excessive cooling when sitting on the seat, especially when perspiring heavily.
To resolve this drawback and consequently limit the initial heat exchange, it is preferable to adopt a “passive” solution, i.e. one without a fan, for which the user's initial sensation of the seat is essentially determined by the characteristics of the seat upholstery covering.
In this field of solutions, the need is felt to create a seat that is also effective from the heat exchange viewpoint in stationary conditions, where the sensation perceived by the user depends on the capability to dissipate both heat and humidity due to perspiration in an adequate and continuous manner. In the absence of a fan, this dissipation capability is a function of the characteristics of each component of the squab and the backrest, and of the particular combination and arrangement of the components themselves.
In the embodiments without fan, the seat upholstery covering is formed by an external fabric layer and an internal layer, made of a plastic material foam, which can not adequately dissipate the humidity due to perspiration and confer the desired comfort.
In order to reach such goals, U.S. patent application having publication number U.S. 2004189061 discloses a seat which has, under the fabric layer, an air-conditioning layer comprising a hygroscopic layer. The hygroscopic characteristics are conferred by active carbons in a base material, which is defined by a plastic material foam. The fabric layer preferably is not laminated, i.e. it is not heat-fixed to the below layer, because the lamination of the fabric layer would result in a severe reduction of the permeability. Such reduction would be basically due to the melted plastic material defining the joining between the inner surface of the fabric layer and the hygroscopic layer. Instead of lamination, patent application U.S. 2004189061 suggests therefore to fix the fabric layer to the below layer by sewing.
The need is felt to use a hygroscopic layer without active carbons and to heat-fix the fabric layer to such hygroscopic layer, for example by means of a flame process, without excessively losing the permeability characteristics of the seat upholstery covering.